767 research outputs found
PEPSI deep spectra. II. Gaia benchmark stars and other M-K standards
We provide a homogeneous library of high-resolution, high-S/N spectra for 48
bright AFGKM stars, some of them approaching the quality of solar-flux spectra.
Our sample includes the northern Gaia benchmark stars, some solar analogs, and
some other bright Morgan-Keenan (M-K) spectral standards. Well-exposed deep
spectra were created by average-combining individual exposures. The
data-reduction process relies on adaptive selection of parameters by using
statistical inference and robust estimators.We employed spectrum synthesis
techniques and statistics tools in order to characterize the spectra and give a
first quick look at some of the science cases possible. With an average
spectral resolution of R=220,000 (1.36 km/s), a continuous wavelength coverage
from 383 nm to 912 nm, and S/N of between 70:1 for the faintest star in the
extreme blue and 6,000:1 for the brightest star in the red, these spectra are
now made public for further data mining and analysis. Preliminary results
include new stellar parameters for 70 Vir and alpha Tau, the detection of the
rare-earth element dysprosium and the heavy elements uranium, thorium and
neodymium in several RGB stars, and the use of the 12C to 13C isotope ratio for
age-related determinations. We also found Arcturus to exhibit few-percent CaII
H&K and H-alpha residual profile changes with respect to the KPNO atlas taken
in 1999.Comment: in press, 15 pages, 7 figures, data available from pepsi.aip.d
PEPSI deep spectra. I. The Sun-as-a-star
As part of the first Potsdam Echelle Polarimetric and Spectroscopic
Instrument (PEPSI) key-science project, we aim to provide well-exposed (viz.
deep) high-resolution spectra of representative stellar targets. These spectra
will be made available in form of (electronic) atlases. The first star in this
series of papers is our Sun. It also acts as a system-performance cornerstone.
The deep spectra in this paper are the results of combining up to 100
consecutive exposures per wavelength setting and are compared with other solar
flux atlases. Our software for the optimal data extraction and reduction of
PEPSI spectra is described and verified with the solar data. Three deep solar
flux spectra with a spectral resolution of up to 270,000, a continuous
wavelength coverage from 383 nm to 914 nm, and a photon signal to noise ratio
(S/N) of between 2,000-8,000:1 depending on wavelength are presented.
Additionally, a time-series of 996 high-cadence spectra in one cross disperser
is used to search for intrinsic solar modulations. The wavelength calibration
based on Th-Ar exposures and simultaneous Fabry-Perot combs enables an absolute
wavelength solution within 10 m/s (rms) with respect to the HARPS laser-comb
solar atlas and a relative rms of 1.2 m/s for one day. For science
demonstration, we redetermined the disk-average solar Li abundance to
1.09+/-0.04 dex on the basis of 3D NLTE model atmospheres. We detected
disk-averaged p-mode RV oscillations with a full amplitude of 47 cm/s at 5.5
min. Comparisons with two solar FTS atlases, as well as with the HARPS solar
atlas, validate the PEPSI data product. Now, PEPSI/SDI solar-flux spectra are
being taken with a sampling of one deep spectrum per day, and are supposed to
continue a full magnetic cycle of the Sun.Comment: in press, 13 pages, 8 figures, data available from pepsi.aip.d
Chemical Composition of the RS CVn-TYPE Star Lambda Andromedae
Photospheric parameters and chemical composition are determined for the
single-lined chromospherically active RS CVn-type star {\lambda} And (HD
222107). From the high resolution spectra obtained on the Nordic Optical
Telescope, abundances of 22 chemical elements and isotopes, including such key
elements as 12C, 13C, N and O, were investigated. The differential line
analysis with the MARCS model atmospheres gives T eff=4830 K, log g=2.8,
[Fe/H]=-0.53, [C/Fe]=0.09, [N/Fe]=0.35, [O/Fe]=0.45, C/N=2.21, 12C/13C = 14.
The value of 12C/13C ratio for a star of the RS CVn-type is determined for the
first time, and its low value gives a hint that extra-mixing processes may
start acting in low-mass chromospherically active stars below the bump of the
luminosity function of red giants
Chemical Composition of the RS CVn-type Star 29 Draconis
Photospheric parameters and chemical composition are determined for the
single-lined chromospherically active RS CVn-type star 29 Draconis (HD 160538).
From the high resolution spectra obtained on the Nordic Optical Telescope,
abundances of 22 chemical elements, including the key elements such as 12C,
13C, N and O, were investigated. The differential line analysis with the MARCS
model atmospheres gives Teff=4720 K, log g=2.5, Fe/H]=-0.20, [C/Fe]=-0.14,
[N/Fe]=0.08, [O/Fe]=-0.04, C/N=2.40, 12C/13C=16. The low value of the 12C/13C
ratio gives a hint that extra mixing processes in low-mass chromospherically
active stars may start earlier than the theory of stellar evolution predicts
Non-Universality of the Specific Heat in Glass Forming Systems
We present new simulation results for the specific heat in a classical model
of a binary mixture glass-former in two dimensions. We show that in addition to
the formerly observed specific heat peak there is a second peak at lower
temperatures which was not observable in earlier simulations. This is a
surprise, as most texts on the glass transition expect a single specific heat
peak. We explain the physics of the two specific heat peaks by the
micro-melting of two types of clusters. While this physics is easily
accessible, the consequences are that one should not expect any universality in
the temperature dependence of the specific heat in glass formers
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